What are the steps to verify a false positive result for benzoylecgonine (Benzoyl Ecgonine), a metabolite of cocaine?

From the Guidelines

To verify a false positive result for benzoylecgonine, it is essential to request a confirmatory test using gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). This approach is crucial because initial immunoassay screenings are susceptible to cross-reactions, resulting in false-positive results, as noted in studies such as 1. The use of GC-MS or LC-MS/MS for confirmation can positively identify a substance and generate quantitative concentrations, thereby reducing the likelihood of false positives.

When verifying a false positive result, several steps can be taken:

• Inform the laboratory about any medications being taken that could cause false positives, such as certain antibiotics (fluoroquinolones), pain medications, or some over-the-counter cold remedies, as highlighted in 1.
• Document all prescription and non-prescription substances consumed in the days before testing to help identify potential sources of cross-reactivity.
• Consider requesting a hair follicle test as an alternative confirmation method, which can detect cocaine use over a longer period.
• If necessary, arrange for observed collection of a new sample to eliminate concerns about sample tampering or substitution.

False positives can occur due to cross-reactivity with structurally similar compounds, laboratory errors, or contamination, as discussed in 1 and 1. Immunoassay screening tests are designed for sensitivity rather than specificity, which is why confirmatory testing is essential when accuracy is critical for employment, legal, or medical decisions. By prioritizing the use of more specific and sensitive testing methods like GC-MS or LC-MS/MS, as recommended by the most recent and highest quality studies, the risk of false positives can be significantly reduced, thereby protecting the individual's rights and ensuring that decisions are based on accurate information.

From the Research

Verification of False Positive Benzoylecgonine Results

To verify a false positive result for benzoylecgonine, the following steps can be taken:

• Confirmatory testing using gas chromatography-mass spectrometry (GC-MS) can be performed to verify the presence or absence of benzoylecgonine in the urine specimen 2.
• The use of pentafluoropropionyl derivative can help eliminate interference from other substances, such as fluconazole, which can cause false-negative results in GC-MS confirmation tests 3.
• Testing for parent cocaine in addition to benzoylecgonine can also help identify false-negative results, as some individuals may have recently administered cocaine or have impaired metabolism 4.

Potential Causes of False Positive Results

Some potential causes of false positive results for benzoylecgonine include:

• Cross-reactivity with other substances, although studies have shown that some immunoassays have high selectivity and do not exhibit cross-reactivity with other drugs 5.
• Interference from other substances, such as fluconazole, which can be eliminated using pentafluoropropionyl derivative 3.
• Limitations of immunoassay-based screening methods, which can produce false-positive results, highlighting the need for confirmatory testing using more sensitive and specific analytical techniques, such as GC-MS 2.

Importance of Confirmatory Testing

Confirmatory testing is crucial in verifying the presence or absence of benzoylecgonine in urine specimens, as false-positive results can have significant clinical and forensic implications:

• False-positive results can impact patient management, including pain therapy and treatment options 2.
• False-negative results can also have profound impacts, such as delayed referral to addiction treatment or unintentional prescribing of controlled substances 4.